1. Field of the Invention
The present invention relates to a technology of extracting a micro-sample from a specimen substrate, i.e., a technology of separating, extracting, and storing of the micro-sample. More particularly, the present invention relates to a method and an equipment for separating and extracting a micro-sample including a specific region from a specimen substrate, and for storing it.
2. Description of the Related Prior Arts
In recent years, in a structure analysis of semiconductor devices, there has been demanded an observation of a very minute structure which is so small that, at a resolving power of an ordinary scanning electron microscope (hereinafter, abbreviated as an SEM), the structure cannot be observed any longer. As a result, observation by means of a transmission electron microscope (hereinafter, abbreviated as a TEM) is indispensable in place of an SEM. As for the fabrication of an observation micro-sample to be used for TEM observation, there is a method described in WO99/05506 (cited reference 1). With the method described in the foregoing cited reference 1, first, the periphery of a region desired to be subjected to an analysis on a specimen substrate (hereinafter, referred to as an observation region) is subjected to ion beam sputtering processing, thereby defining and forming the observation region. Then, the tip of a probe is firmly joined to the observation region thus defined and formed. Subsequently, in order to separate the observation region from the specimen substrate, ion beam sputtering processing is performed thereon to separate and extract a micro-sample including the observation region from the specimen substrate. Then, the micro-sample separated and extracted while being firmly joined to the probe tip is transferred to a position at which a sample holder exists. The extracted micro-sample is then fixed on the sample holder. Thus, the probe tip is cut off from the micro-sample by an ion beam sputtering method. With the foregoing operation, separation and extraction of the micro-sample, and firm attachment (storing) of the micro-sample onto the sample holder are completed. Thereafter, a desired observation, analysis, and measurement are performed on the observation region on the micro-sample which has been cut off from the probe tip and firmly attached on the sample holder.
Further, as another method, in Japanese Published Unexamined Patent Application No. Hei 8-132363 (cited reference 2), there is proposed a two-finger microhand mechanism whereby a minute micro-sample is held by effecting extension and contraction of two hands by piezoelectric elements by means of a parallel linkage. As still other method, in Japanese Published Unexamined Patent Application No. Hei 3-154784 (cited reference 3), there is proposed a tweezers mechanism using bimorph type piezoelectric elements as driving sources. With either of these methods, the micro-sample is held by moving the hands or tweezers by using piezoelectric elements.
Further, in the section in the literature (cited reference 4) entitled xe2x80x9cSpecimen Preparation for Transmission Electron Microscopy of Materials IVxe2x80x9d on pages 19 to 27 of Material Research Society (MRS) Symposium Proceedings, vol. 480, L. A. Giannuzzi et. al., disclose a Lift-Out method. With this method, a thin specimen portion for TEM observation is formed in a specimen substrate by using an FIB (Focused Ion Beam) (corresponding to the steps of FIGS. 21A to 21G). After formation of the thin specimen portion, the specimen substrate is taken out into the air, and placed under an optical microscope. Thus, a sharpened glass rod is brought to the proximity of the thin specimen portion. Then, the sharpened tip of the glass rod is pressed against a part of the thin specimen portion to separate the thin specimen portion from the specimen substrate. Further, the tip of the same glass rod is brought to the proximity of the separated thin specimen portion. Accordingly, the thin specimen portion is allowed to electrostatically adsorb to the glass rod tip by the static electroricity occurring at the glass rod tip. The thin specimen portion adsorbed and held on the glass rod tip is transferred onto a carbon film-coated hollow grid, and the thin specimen portion is attached to, and held by the hollow grid so as to face the carbon film. The hollow grid holding the thin specimen portion is introduced into a specimen chamber of a TEM to permit the TEM observation of the thin specimen portion.
Still further, in WO99/17103 (cited reference 5), mention is made of the use of tweezers for extracting a micro-sample. However, neither disclosure nor suggestion is made on the mechanism or the structure of the ones referred to as the tweezers.
The foregoing prior art technologies have the problems as shown below.
A first problem is in that contamination may be caused on the micro-sample and the specimen substrate upon extracting the micro-sample. In the prior art technology disclosed in the cited reference 1 described above, when the probe tip is firmly joined to the vicinity of the observation region of the specimen substrate, the firm joining therebetween is established through an ion beam assisted deposition film (hereinafter, referred to as a deposition film) or an ion beam sputtered particle redeposition film. This entails the following problem. When an assist gas to be the raw material for the deposition film is supplied, the observation region in the micro-sample and the neighboring region thereof are contaminated by the assist gas. The region which has been once contaminated is difficult to define. Further, it also causes failures in the subsequent and later steps. Still further, the contaminated region may also be expanded according to the steps. In such a case, unfavorably, the specimen substrate cannot be used for observation or analysis in the subsequent and later steps any longer.
A second problem is a problem associated with the extraction of the micro-sample. The cited reference 1 has a description to the effect that an electrostatic adsorption method may be used as the method for firmly joining the probe tip to the micro-sample. Further, the method in which the micro-sample is held by utilizing the electrostatic adsorption force at the glass rod tip is known as the Lift-Out method (the cited reference 4). With this method, there occurs no problem of contamination on the micro-sample because the electrostatic adsorption method is used. However, since the micro-sample is minute, a sufficient electrostatic force cannot be given thereto. Accordingly, the micro-sample is difficult to hold with stability. Specifically, with this method, when the separated minute micro-sample is transferred onto the grid, the specimen substrate is taken out into the air (into a laboratory), and then the micro-sample is electrostatically adsorbed to the glass rod tip. Therefore, the electrostatic adsorption force of the micro-sample to the glass rod tip largely depends on the humidity in the laboratory. For this reason, it may happen that, the micro-sample cannot be adsorbed to be separated and extracted from the specimen substrate, or the micro-sample is dropped during transfer onto the grid. This results in a very low probability (success rate) that the micro-sample can be ideally attached onto the carbon film. Further, the thin specimen is not always adsorbed to the tip of the glass rod, and it is often attached to the side of the glass rod according to the distribution of the generated electrostatic force. In this case, it is not possible to attach the micro-sample onto the carbon film-coated surface on the grid. Once the micro-sample is adsorbed to the side of the glass rod, the micro-sample cannot be transferred to the tip of the glass rod afterward because the micro-sample is a thin piece with very minute dimensions of about several micrometers to ten and several micrometers per side. After all, the micro-sample cannot be attached onto the carbon film-coated surface of the grid, and hence it cannot be made available for use as a TEM specimen. Particularly, in the failure analysis of a semiconductor device, the site to be noted as the observation region is determined. Therefore, the micro-sample to be extracted can be said to be unique. Accordingly, with the method for separating and extracting the micro-sample utilizing the electrostatic adsorption force to the glass rod, the probability is low that a specimen which can be made available for use as a TEM specimen can be obtained. Such a low reliability specimen fabrication method may be inapplicable to the failure analysis of a very minute structured element of a semiconductor integrated circuit or the like. Further, with the method utilizing the static electricity, on the contrary, even the following case could occur: the minute micro-sample is flicked to an undesired site by a repulsive force due to the static electricity, so that the important micro-sample is lost. Thus, unfavorably, the method utilizing the electrostatic adsorption force becomes the very unreliable method for holding a micro-sample.
A third problem is a problem associated with the working efficiency during extraction of a micro-sample, i.e., the throughput, and the equipment configuration. The two-finger microhand mechanism described in the cited reference 2 adopts a method for holding a minute micro-sample by two microhands with a high degree of freedom. However, with this method, the two microhands are required to be positioned and set so as to allow holding of the micro-sample with precision. This operation is complicated, and requires a skill. This presents a large obstacle to practical use thereof. Specifically, with such a mechanism for holding a minute micro-sample in micrometers as the two-finger microhand mechanism, a movable beam having an independent configuration is required to be used. Since the micro-sample serving as an object to be held is a very minute thin piece with a size in micrometers, the tip of the movable beam as a hold system for holding this is also required to have a size in micrometers. Therefore, also for the alignment of the hold system tip, a very high alignment precision in units of micrometers or in smaller units is inevitably required. The act of performing such a high precision alignment by using two independent movable beams involves the operation which is very complicated, and requires a skill. Further, with the method for holding the very minute micro-sample by the two-finger microhand system of the independent movable beams, it is required to manipulate and control the holding force for holding the micro-sample and the relative positional relationship between respective contact positions of the two microhands with the micro-sample. This also results in an operational problem of the lack in the stability and the reliability during holding of the micro-sample. Still further, as a mechanical problem, since a parallel linkage using piezo elements as driving sources is used, also unfavorably, the equipment configuration increases in scale.
Further, the tweezers mechanism described in the cited reference 3 also has a problem that the operation which is complicated and requires a skill is unavoidable for holding a micro-sample as with the method described in the cited reference 2. Still further, with the tweezers mechanism described in the cited reference 3, bimorph type piezoelectric elements are used as the driving sources. Therefore, it cannot choose but to place the tweezers mechanism for holding the micro-sample and the bimorph type piezoelectric elements for driving the tweezers mechanism at mutually separated positions. In consequence, unfavorably, it is difficult to ensure the operation precision required for holding a minute micro-sample in micrometers.
For these reasons, with the prior art technologies, it is very difficult to extract a very minute micro-sample in micrometers without contaminating the micro-sample and/or the neighboring region, and hold the minute micro-sample with precision and stability at the same time.
The present invention has been completed in view of the forgoing problems in the prior art. It is therefore an object of the present invention to provide an equipment and a method capable of stably separating, extracting, and storing a very minute micro-sample with precision and a high throughput without contaminating the very minute micro-sample and/or the peripheral region.
Namely, in accordance with the present invention, there are provided a means and a method for minimizing the contamination of the peripheral region of a minute micro-sample when the micro-sample is extracted from the specimen, and holding and extracting, and further storing it with precision and stability.
An equipment for specimen fabrication in accordance with one example of the present invention is configured by including: a stage movable with a specimen substrate mounted thereon; an ion beam irradiating optical system made up of an ion source for generating an ion beam, and an ion beam optical system for irradiating the ion beam to a prescribed position on the specimen substrate; a beam made up of a rod-like member having a shape in which its tip is formed thinner as compared with its root, and the tip is split into two units, for holding a micro-sample portion to be separated and extracted by pressing into the specimen substrate, and then separating and extracting the micro-sample portion from the specimen substrate by pulling it out of the specimen substrate; a sample hold system including the beam at its tip, and being capable of rotating the beam; a transfer system for transferring the sample hold system relative to the specimen substrate; a contact detection system for detecting the contact state between the beam and the micro-sample; and a vacuum chamber for accommodating the whole of these components.
Then, a description will be given to one example of a method for separating and extracting a minute micro-sample from the top of the specimen substrate, and storing it in a prescribed place by using the foregoing equipment for specimen fabrication in accordance with one example of the present invention.
First, as a first step, the specimen substrate is mounted on the stage to determine an observation region (a portion to be separated and extracted as a micro-sample). Subsequently, a part of the peripheral portion is left as a residual area, and the observation region is processed into a micro-sample shape to be able to be separated and extracted by an ion sputtering method.
Then, as a second step, the micro-sample being connected to (temporarily held by) the specimen substrate by the residual area is held by pressing the micro-sample portion into the tip split into two units, of the beam made up of the rod-like member so configured that its tip is formed thinner as compared with its root, and the tip is split into two units (hereinafter, beam), attached at the tip of the sample hold system. Then, the beam is pull out of the specimen substrate, and thereby, the micro-sample portion is separated from the specimen substrate. Namely, upon holding the micro-sample, holding is achieved by moving the rod-like member so as to insert the micro-sample into the portion in the shape in which the tip is split into two units while extending the portion by force.
Then, as a third step, the specimen held by the beam is formed into the micro-sample separated from the specimen substrate by removing the residual area by an ion beam sputtering method.
Then, as a fourth step, the micro-sample held by the returning force (restoring force) of the beam is extracted from the specimen substrate by relatively moving the sample hold system or the specimen stage.
Further, in a fifth step and later steps, in accordance with the objects and the necessities, it is possible to subject the micro-sample separated and extracted by the foregoing steps up to the fourth step to analysis, observation, processing, and the like. Herein, as a typical example thereof, a description will be given to a method for manufacturing a micro-sample for observation in order to perform TEM observation.
Namely, as a fifth step, the micro-sample separated and extracted by the previous fourth step is rotated to a given angle by the function of rotating the beam provided to the sample hold system. By using the rotary function, if required, the micro-sample is rotated to a given angle, and subjected to additional processing into a micro-sample shape preferable for TEM observation by an ion beam sputtering method. Examples of the additional processing into a micro-sample shape preferable for TEM observation include the processing of a part or the whole of the separated and extracted micro-sample into a micro-sample shape thinned to a thickness capable of TEM observation. Incidentally, the fifth step may be carried out, if required. This step is not required to be carried out when the micro-sample is thinned by another method or step, or in other cases. For example, when the micro-sample is thinned by using an ion beam sputtering method after holding the micro-sample on the micro-sample holder in a sixth step and later steps described below, additional thinning processing is not required to be carried out in this fifth step.
Then, in a sixth step, for example, the micro-sample is mounted on the micro-sample holder for TEM observation disposed on the specimen stage. There are the micro-sample holders for TEM observation, having various configurations. Appropriately, an appropriate mounting method should be adopted according to the configuration of the holder. For example, in the present invention, a holder with a trench for insertion of the micro-sample into which the micro-sample can be inserted is provided in advance by an ion beam sputtering method. Then, by the beam, the micro-sample held by it through the returning force of the beam itself is transferred to the trench for insertion of the micro-sample on the micro-sample holder. Then, the micro-sample is inserted and fixed in the trench, and thus the beam is transferred in such a direction that the micro-sample will not come out of the trench. As a result, the micro-sample and the beam are separated from each other, allowing the micro-sample to be mounted on the holder. Other than this, mounting of the micro-sample on the holder is accomplished in the following manner. For example, an ion beam assisted deposition film (deposition film) is formed at the contact portion between the micro-sample and the holder. The micro-sample is firmly joined onto the holder by this deposition film. Then, the sample hold system is operated, so that the beam and the micro-sample are relatively moved. In consequence, the beam and the micro-sample are separated from each other. This separation can also be accomplished by adopting the following method. Namely, with a part of the micro-sample firmly joined onto the holder, a part of the beam holding the micro-sample (micro-sample holding portion) is cut by an ion beam sputtering method, so that the micro-sample and the beam are separated (detached) from each other. Incidentally, it is also possible to carry out the foregoing steps up to the sixth step in a vacuum chamber (namely, in a vacuum atmosphere). Namely, it is possible to carry out all the steps of from the step of determining the portion desired to be observed on the specimen substrate, and holding and extracting the observation region by the physical force from the specimen substrate as the micro-sample, to the step of subjecting it to thinning processing as the TEM specimen in the vacuum chamber.
A seventh step is a step of extracting the micro-sample mounted on the sample holder together with the holder from the specimen fabrication equipment, and performing desired analysis, observation, measurement, and the like with respect to the micro-sample by using a TEM apparatus disposed together with or separately from the specimen fabrication equipment.
Incidentally, in the fifth step and later steps described above, it is possible to fabricate micro-samples in accordance with apparatuses for performing various other analyses, observations, measurements, and the like by using the same method, not limited to fabrication of the micro-sample for TEM observation. Further, in the foregoing fifth step, by using a rotary system disposed in the sample hold system for the micro-sample held by the beam, it is possible to rotate the micro-sample to a given desired angle, and to perform analysis, observation, measurement, and the like, on the spot. Still further, by adopting an additional processing method of the micro-sample by an ion sputtering method for performing the analysis, observation, measurement, and the like, it is also possible to perform the analysis, observation, and measurement while arbitrarily subjecting the micro-sample to additional processing, and to use the secondary products such as secondary ions, neutral particles, and an X-ray occurring upon the additional processing for analysis and observation. Still further, in the previous fourth step and later steps, the sample hold system or the beam holding the micro-sample is so configured as to be separable and detachable from the specimen fabrication equipment main body. In addition, the sample hold system or the beam is used in common for holding the specimens for other analysis apparatuses or the like, typically such as the TEM apparatus. In consequence, it is also possible that the micro-sample separated and extracted from the specimen substrate is analyzed, observed, and measured with these other analysis apparatuses. In this case, it is possible not only to shorten the analysis time, but also to perform reprocessing or additional processing of the micro-sample by using an ion beam sputtering method by mounting it in the specimen fabrication (processing) equipment again after analysis, observation, and measurement with these other analysis apparatuses.
Then, a description will be given to the configuration, function, and the like of the beam used in the foregoing method. As described in the paragraph of the prior art, for holding the minute micro-sample by two independent movable beams in accordance with the prior art method, a high precision alignment operation of the movable beam tips is required. In addition, as described previously, unfavorably, the minute micro-sample is difficult to hold with reliability. In contrast, in the present invention, the alignment of the beam tip for holding the micro-sample is essentially unnecessary. Further, it is possible to hold the micro-sample with reliability. As a specific method, the micro-sample sandwiched in the beam tip, and thus extracted from the specimen substrate is inserted and held in the trench for insertion of the micro-sample disposed on the sample holder. Thus, the micro-sample is pulled out of and separated (detached) from the beam. The beam is a beam made up of a rod-like member having a shape in which its tip is formed thinner as compared with its root, and the tip is split into two units. By sandwiching and holding the micro-sample between the beam tip split into two units, the micro-sample is held through the elastic deformation force of the beam tip without using a piezoelectric element or the like.
As a method for manufacturing the beam, specifically, the rod-like member is previously subjected to narrowing processing so that its tip diameter is about several micrometers by using an electropolishing method or an etching processing method. Further, the narrowed beam tip is subjected to slit processing by an ion beam sputtering method, thereby forming a beam with its tip branched into a plurality of (generally two) units. At this step, the current value of the irradiated ion beam is increased for rough processing, while the current value is reduced for finishing processing. This allows precision processing. The previously electropolished probe (beam) is accommodated in an ion beam processing apparatus. According to the purpose, the probe tip can be processed into a given shape. The beam is processed into such a shape in which the tip has a plurality of branch units. By pressing (inserting) a minute micro-sample in between the plurality of the branch units of the beam, the minute micro-sample is held therein. The micro-sample held between a plurality of the branch units in this manner is held in a sandwiched manner through a restoring force generated by the elastic deformation of the beam itself (i.e., the branch units themselves). This allows reliable and stable holding of the micro-sample. Incidentally, the slit processed and formed at the beam tip by an ion beam sputtering method is more desirably formed into a shape in which the slit width of the slit entrance is larger than the slit width of the slit inside for facilitating insertion of the micro-sample thereinto.
As described above, by adopting the beam having the foregoing configuration in accordance with the present invention as a means for holding the micro-sample, it is possible to easily obtain the beam for holding a very minute micro-sample by the configuration and the manufacturing method. Further, a plurality of the tip branch units and the beam main body are integrally formed in one piece by performing the foregoing slit processing on the beam tip. Therefore, as compared with the case where other objects are joined together as the tip branch units to configure a plurality of tip branch units, alignment of the beam tip for holding the minute micro-sample is not required at all.
With the method of the present invention, it is possible to fabricate a beam having two tip branch units, as one specific example of the configuration of the beam, which has two tip branch units, wherein a slit for insertion of the micro-sample, with a width W of 2 xcexcm and a length L of 30 xcexcm, is disposed between both the tip branch units, and the tip diameter S and the root diameter X of the each tip branch unit are processed and formed to be 1 xcexcm and 3.5 xcexcm, respectively. Therefore, the beam having the forgoing configuration in accordance with the present invention can solve the problems in holding of a micro-sample in the prior art. Further, for holding the minute micro-sample, the elastic deformation force occurring in the tip branch units themselves with sandwiching of the micro-sample in between the tip branch units is utilized, and a deposition film formation method through irradiation with an ion beam is not used for holding the micro-sample as in the prior art. Therefore, there are no factors causing contamination of the micro-sample. In other words, in principle, there occur no factors causing contamination on the micro-sample sandwiched and held between the tip branch units of the beam in accordance with the present invention, and its neighboring region. In addition, the micro-sample hold means in accordance with the present invention can implement holding of the micro-sample by the following simple operation. Namely, the micro-sample is inserted in between the tip branch units formed at the beam tip. Thus, by utilizing the elastic deformation force occurring in the tip branch units themselves, the minute micro-sample is held therein in a sandwiched manner. This produces the following effects. Namely, it is possible not only to shorten the time required for holding, extracting, and storing the micro-sample, but also to markedly improve the throughput during the holding operation of the micro-sample. As a result, the productivity of the micro-sample fabrication can be improved. Specifically, with a prior-art method for fabricating a micro-sample for TEM observation, about 1 hour is required between separation and extraction of the micro-sample from the specimen substrate and storing (holding) of it on the holder. Further, about another hour is required for thinning processing of the micro-sample. However, in accordance with the method of the present invention, the time required between extraction of the micro-sample from the specimen substrate and storing (holding) of it on the holder can be shortened to about 30 minutes. Thus, the effect of shortening the time required for specimen fabrication is large.
Other objects and constitutions of the present invention than described above, and the functions and effects resulting therefrom will be obvious successively in the following detailed description by way of examples.